Apparatus for identifying shortwave foreign radio transmitting stations



K. BIEGLER 2,066,089

FYING SHORT WAVE FOREIGN RADIO TRANSMITTING STATIONS Dec. 29, 1936.

APPARATUS FOR IDENTI Filed April 18, 1956 5 Sheets-Sheet 1 nec. 29, 1936. K .BlEGLER 2,066,089

APPARATUS FOR IDENTIFYING SHORT WAVE FOREIGN RADIO TRANSMITTING STATIONS Filed April 18, 1936 3 Sheets-Sheet 2 INVENTOR: 4 M a3@ BY g Z V A. l Sad/ATTORNEY.

K. BIEGLER APPARATUS FOR IDENTIFYING SHORT WAVE FOREIGN RADIO TRANSMITTING STATIONS 5 Sheets-Sheet 5 Dec. 29, 1936.

Filed April 18, 1956 lNVENTO Karl zeglef;

BY l

g:| v (i l 'I HIS ATTORNEY Patented Dec. 29, 1936 UNITED STATES APPARATUS FOR IDENTIFYING SHORT- WAVE FOREIGN RADIO TRANSIIIITTING STATIONS Karl Biegler, Brooklyn, N. Y.

Application April 18, 1936, Serial No. 75,050

16 Claims.

This invention relates to geographic station indicators for radio receiving sets, more particularly to indicators for short-wave broadcasting stations located in a country foreign to that in which the listener is stationed andhas for its particular objects the provision of means for indicating not only the particular country in which a foreign, short-wave, broadcasting station Whose signals are being received is located 10 but also the particular station in that country,

besides incidentally facilitating the accurate tuning-in of such station. Other objects of the invention will hereinafter appear.

I am aware that it has been proposed, as set forth in Patent No. 1,837,948, to provide co-operating perforated screens on the front of a radio cabinet, the inner one being slidable in consonance with the rotation of the shaft of the tuning condenser to which it is geared n through a ratchet and pinion and the outer screen being stationary and that, when a particular station sought is accurately tuned in, a corresponding aperture in each such screen will be in exact registration so as to permit light beams projected from a source of light within the cabinet to be projected through the registering aperture in the outer screen.

In the accompanying drawings in which I have illustrated a preferred embodiment of my invention Figure 1 is an enlarged, fragmentary, vertical section, partly in elevation, of a radio receiving set equipped with my improved station indicator;

Fig. 2 is a front elevation of the cabinet of such set;

Fig. 3 is a fragmentary, detail front elevation of such cabinet, partly broken away, showing the perforated stationary map dial and the associated rotatable perforated disc;

Fig. 4 is an enlarged detail front elevation of a portion of said rotatable perforated disc showing the different scales displayed thereon;

Fig. 5 is a fragmentary vertical section showing a modified map dial which is studded with jewels or miniature lenses; and

Fig. 6 is a plan View of the rotatable disc.

Fig. '7 is a front elevation of the map dial and its associated movable translucent disc, isolated ,.0 from the cabinet, but showing a modified arrangement of same; and

Fig. 8 is a. fragmentary vertical section of such modified construction and corresponding generally to Fig. 1.

Referring to the drawings and the construction shown therein, the reference numeral I designates the cabinet of an all-wave radio receiving set, 2 the front panel thereof, 3 the loud speaker grill, 4 the knob of the cut-olf switch, 5 the volume control knob, 6 the tuning knob, 'I the band- 5 selector knob and 8 the tone-control knob.

The shaft Ill of the variable tuning condenser, which serves to rotate the plates II thereof, is equipped with -a spurgear I2, that is rigidly mounted on the extreme end thereof, and also a 10 180 sector member I3 which is rigidly mounted on said shaft immediately adjacent and to the rear of said gear. A pressed metal recessed shell I4, having a circular flange or rim I4', is mounted adjacent the front of said cabinet, the same having a central bushing I5, secured thereto by means of screws I6, through which projects a stub shaft I'I. On the inner end of the latterI shaft a co-operating spur gear I8 is rigidly mounted, the same having one-half of the number of teeth of that of spur gear I2. A flanged sleeve I9, which is pinned to the outer end of the same shaft, serves in co-operation with the gear I8 to prevent endwise movement of said shaft in the bushing I5.

A rotatable, translucent disc 20, having perforations a, is concentrlcally mounted on the end of the bushing I9, said disc being provided with a central opening to admit of the reception of the outer end of the stub shaft I1. A cooperating, stationary map dial 2I, formed of opaque material, preferably of metal, and having perforations b and c pierced therethrough, is secured to the frame of said cabinet so that the same rests snugly against the front face of said circular rim I 4'.

A pin 22, which projects through said dial 2|, serves as a journal for the front end of a stub shaft I 'I that is provided with a co-operating cylindrical recess for the reception thereof. A bezel |26, mounted in an annular insert 23 carried by the panel 2, surrounds the said map dial. Said insert 23 is provided with a top and bottom extensions 24 and 25, the former extension as well as the map dial having relatively wide arcuate slots 26, 26', which respectively intersect central vertical slots 21, 21', and the latter extension, as well as the map dial, having relatively narrow arcuate slots 28, 28', respectively. Said bezel is marginally grooved to receive a transparent lens member 29.

The inner concave surface d of the metal bezel |26 and the outer surface e of the metal shell I4 constitute mirrors, being preferably chromium plated, and as a consequence will refleet light rays projected from electric lamps or bulbs 20 that may impinge thereon, such rays being either projected through the apertures c and then reilected from the mirror d across the face of the dial or being projected through the apertures b of the map dial when the latter are in registry with aperture a of the disc. Furthermore, the rays from the lamps or bulbs In, intensiiied by reflection from the mirror e, will produce a glow, preferably reddish, corresponding to the color of the translucent disc 2l which will be visible to the observer through the apertures b of the map dial when the same are out of register with the apertures a of the disc and which will be also visible to the observer through the portion of the marginal bands Ion disc 2l which are observable through the apertures 2i,

26 and 21, 21', thereby enabling the observer` to ascertain the frequency, call letter or wave length of the particular station which is being received as indicated on the portion of such marginal bands which are visible through such apertures 26, 26 and 21, 21'.

A stub shaft 35, on which the tuning button 6 is mounted, extends through the front oi' the cabinet and through the front panel and the frame of the cabinet, the same being rotatably mounted in a bearing 36 carried by the chassis 31. A gear pinion 38 is rigidly mounted on the rear end of said shaft 3l and such pinion meshes with the marginal teeth on the 180 sector I3.

The rotatable disc 20 is provided with a series of concentrically disposed bands comprising a long-wave frequency band 4II, calibrated in kilocycles, a. short-wave band 4I (amateur and police calls) preferably of a special color such as yellow and calibrated in megocycles, another wave-length band 42 preferably colored red at appropriate intervals and calibrated in meters and a second short-wave frequency band 43 (foreign broadcast), preferably colored green and also calibrated in megocycles, while at the extreme margin of the disc is a band 44 on which the call letters of the various foreign short-wave stations, in radial arrangement reading from the margin inwardly, are disposed.

In the construction illustrated in Fig. 5, the apertures b are studded with colorless jewels f which serve to concentrate and further intensify the light beam transmitted to the eye of the observer. t

In Figs. 7 and 8, there is illustrated a modiiled form of construction wherein the map dial and associated translucent disc are eccentrically disposed with respect to each other, which admits of the indicator being at least as visually selective as the audible selectivity of the most sensitive set, since it is apparent upon analyzing same that the annuli described throughthe same cities as in Fig. 6 would be of greater radius, being described from a more remote center and consequently of considerably greater circumference, so that the stations represented by apertures disposed on the various annuli of the movable disc shown in Fig. '7 are spaced at a greater peripheral distance from each other than would be the apertures representing like stations on the annuli of the movable disc of Fig. 6.

In this modified construction shown in Figs. 7 and 8, the parts having identical reference characters to those shown in Figs. 1 and 3, are identical therewith, but the gears I2', I0 and the 180 sector I3 are all a different size as compared with the gears I2, I 3, and I8 of Fig. 1, this being necessary because of the diiferent location of the shafts Il and I1, but the gear ratio is such that the shaft Il moves at double the speed of the condenser shaft I0, the same as in the case of the construction shown in Fig. 1. 'Ihe reference numeral |40, shown in Fig. 8 designates the l peripheral ange which is formed on the recessed the same as in the case of the map dial shown in Fig. 1.

The imaginary annuli x', u' and z' shown in Fig. 8 along which dot-like means a are disposed and which dot-like means dispod along each particular rannulus represents short wave transmitting stations of a single foreign country which is dierent from the foreign country represented by the dot-like means on any other annulus. In the particular map shown in Fig. 8, the dot-like means on the annulus zwill, when the movable disc or screen is rotated, be brought into registry with the aperture b at Madrid, Spain, which latter is common to the Spanish transmitting stations; the dot-like means or annulus u can likewise be brought into registry with the aperture b at Mexico City, Mexico, which is common to the Mexican transmitting stations; and the dot-like means or annulus z' can also be brought into registry with the aperture b at Tokyo, Japan, which is common to the Japanese transmitting stations. i

To operate the set to bring in a foreign shortwave station, the switch 4 is turned on, the volume control is preferably cut down to nil, 'the tuning condenser is thenrotatably adjusted by rotating knob 6 until the desired wave length frequency or call .letters of the particular station sought, appear through the slots 2l, 29 or 3l. Thereby the approximate or rough tuningg in of the desired station will have been accomplished. Thereupon, in order to accurately or closely tune-in such station and also in order to enable the operator to identify which station is so brought in, the tuning knob 6 is very slowly turned until the perforations a in the disc 2l which are in approximate registry with the perforations b of the map dial 2I move into accurate registration with each other. Such accurate registration of apertures a and b can be easily ascertained by the observer since the disc 20 is formed of translucent material, preferably bakelite of a reddish color or hue when illuminated, and consequently the rays emitted through the perforations b of the map dial 2|, when the same are out of registration with corresponding perforations a disposed in disc 20 at the same radial distance from the center of the shaft Il, will transmit a diffused reddish glow, while at the moment the corresponding registrations in the discs 20 and 2| commence to come into registration with each other, a two-color or partial eclipse-like efle'ct will occur which'will continue until complete registry occurs, whereupon the red glow will be completely eclipsed and replaced by a brilliant white or yellow light corresponding to that emitted by the bulbs or lamps 4I.

When an aperture a is in complete registration with an aperture b, the observer vwill nd that the white light is being emitted from an aperture -representing one lparticular country, only, and

thereby he'can be certain that it is a station in that particular country from which the signals are being received. Then, by referring to the Wave frequency or the call letters indicated in theslots 26, 26' and 21, 21,1he can ascertain which particular one of the various stations in that particular country is being received by him. Whilea set ,equipped with my improved dial indicator may be .also utilized for -the reception of long-wave broadcasting, no attempt is made to indicate, byvmeans .of registering apertures on the map and'on the rotatable disc 20, which particular long-wave station is being received because, inthe first place the long-wave reception, duev to interference and the difficulty of transmitting long-waves over long distances is limited, in the daytime at least, to an 'area of a radius of 200 miles or less withv the average high quality set now on the market and also because such accurate means of identificationis wholly unnecesary due to the frequent announcements from these local stations of their identity and the fact that the Wave frequencies of these longwave stations are indicated through the slots 28.

The apertures c in the map dial are so disposed with respect to the concave bezel member |26 that a diffused light will be reflected by such bezel across the face of the dial and no direct rays from said lamps will reach the eyes of an observer or operator. However, the face of the map dial proper being visible to the observer through the transparent lens member 29, the light rays transmitted from the lamps through the identifying apetures b in the map dial will, on the other hand, be transmitted directly to the eyes of an observer.

The crux of my invention, insofar as it relates to the identification of short-wave foreign broadcasting stations, resides in the manner in which the annuli are described on the disc 20', namely, so that each annulus represents a single country to be represented on such disc so that, when the latter is rotated, some portion of the imaginary annulus thereon will at all times be directly behind the aperture in the map screen which represents that particular country. Consequently as shown in Fig. 6, each imaginary annulus represents a country which has a plurality of prominent short-wave broadcasting stations and will accordingly have a plurality of perforations therethrough appropriately spaced on said annulus to represent the difference in the frequencies of one station as opposed to another station in the same country. It is possible for the observer to accurately identify several stations in each large country, since it is merely necessary in those cases where several stationsv in a single country are represented on the same'annulus of the rotatable disc, for the observer to refer to the call-letter band when the aperture or perforation in the map dial is illuminated by a pure beam of light corresponding to that emitted by the lamps 30. As shown in Fig. 6, the imaginaryv annulus x is of a radius corresponding to the radial distance from the center of said disc to the center of the aperture in the map dial representing England, whether the center of rotation of the disc coincides with that of the map dial or, as explained herein, is eccentric with respect thereto and positioned outside of the margin of the map dial. Such annulus is pierced with 5 spaced perforations corresponding to nulus z representing France is pierced with 2 apertures corresponding t0 2 different stations of different frequencies. In other words, each annulus of the disc 20 may be provided with as many pierced apertures as corresponds to the l number of stations in a single country repre- "sented by such annulus as it is desired to identify on my improved indicator and as previously stated, even a dozen or more stations in a single country may be represented if desired, particularly if the indicator is rendered ultra-selective by arranging the center of rotation of the disc 20 outside of the margin of the map, i. e., positioned a considerable distance above the center of the map dial, preferably what would represent of latitude (see Figs. 7 and 8).

It is to be understood that a standard map may be illustrated on the map screen or as is preferably the case, certain ofthe smaller countries having important transmitting stations may be enlarged out of proportion to facilitate the avoidance of interference between a beam transmitted through an aperture in a small area representing one country and a beam transmitted through an aperture in a closely contiguous small area, say about 4 /64 distant, representing another country. Or else it may even be found desirable to provide apertures in the map on certain neutral areas as the Mediterranean or the Baltic Sea, etc. and label such apertures to correspond with some small country such as one of the Balkan States which is undesirably located to admit of the map dial being pierced in the map portion on which such country is represented.

While accurate tuning-in of the particular station results when full registration of two corresponding apertures in the map dial 2l and disc 20 is effected, this feautre is only incidental to applicants invention and no claim is made to the mere utilizationof two corresponding apertures in associated discs or screens for the tuning purposes, as such, this feature also being disclosed in said Patent No. 1,837,948 and also Patent No. 1,713,001.

While I am aware that in certain isolated instances short-wave radio transmitting stations in one country may at present operate on the same identical frequency of the radio spectrum, but at different hours, as employed by certain powerful short-wave radio transmitting stations in another country, it is confidently believed that eventually, through some international commission, definite but different frequency channels will be assigned to each country and consequently it will be possible to operate my improved geographic indicator without more than two apertures being in registration at any onetime. Until that time arrives, however, it is desirable to either represent on the rotatable disc but a single one of such different stations of the same -identical frequency and omit the others. In such a case the station which is not represented can be tuned-in in the usual way, by merely rotating the condenser shaft and simultaneously observing the indicated posi- 75 tion thereof as shown on the frequency band or the call-letter band.

In order to calibrate a set equipped with my improved geographical indicator, following lthe manufacture of the same, it is merely necessary for the test engineer in the shop laboratory to accurately tune-in a particular foreign station n the usual way by reference to the megocycle d and then when the identity of such station has been definitely rechecked by reference to the call-letters on the call-letter scale or band and also by listening to the station announcement, a drill is inserted through one of the apertures in the map dial that is disposed in the respective vareas representing each diiferent country that recognized short-wave transmitting or broadcasting stations which the manufacturer believes it may be of interest to receive and then while the rotatable disc is supported at the rear and while such drill is positioned in the aforesaid existing aperture in said map screen, said drill is caused tov penetrate the rotatable disc and form therein an aperture which is of identical size, preferably about 3 /64, with that of the minimum diameter of said aperture in the map dial. Preferably the outer margin of the apertures in the map dial are chamfered or bevelled and the inner margin of each aperture so formed in the rotatable disc is likewise so chamfered or bevelled, in order to' concentrate the rays of light and thereby intensify the beam projected through the aperture in the map dial. Similarly other apertures, to the extent desired, are pierced in the rotatable disc until there is at least one aperture on the rotatable disc that corresponds with a pre-formed or existing aperture in the map screen and, in many cases, as previously stated, two or more such apertures are formed in the rotating disc on the particular annulus which corresponds to a single country to represent the different stations in that particular country which it may be desired to identify by means of my improved geographic indicator.

It is of course to be understood that the within described geographic indicator is also peculiarly adapted for identifying television transmitting stations as well as the ordinary short-wave radio broadcasting stations on future television-radio receiving sets.

My improved station finder serves as an effective band spread, as it were, for enabling the definite and positive identification of a particular foreign broad-casting station. Such band spread efIect can be accomplished either by employing large screens, arranged for example vas shown in Figs. 1 and 3, or by employing a relatively small map dial and a large eccentrically mounted movable screen, suchas shown in Fig. 8. While I prefer to employ disc-like screens, one of which is relatively movable with respect to the other, nevertheless, the term relatively movable screens, as employed in the claims is used in a' appended claims.

Having thus described my invention, what I claim and desire to obtain by United States Letters Patent is:

l. In a radio receiving set, the combination bers of any one group being equi-distant from ak common center and being positioned at intervals along an arc and all of the members of any one group lying in a different arc from those of any other group, a stationary screen having disl played on the front thereof a map representing various foreign countries, several of which have a plurality of short-wave radio transmitting stations located therein, said latter screen having a single perforation only in the map portion thereof that represents a particular country having a plurality of transmitting stations located therein and which stations are represented on said rotatable screen, illumination means for projecting light through said latter screen, means, rotatable simultaneously with the movement of said disc, for rotating said tuning element; and reflector means associated with said illuminating means. l l

2. In a radio receiving set, the combination with the shaft of a variable tuning element of a rotatable screen having a plurality of dot-like means positioned at intervals thereon and each of which is so positioned as to correspond to the frequency of the cycles of the waves transmitted from one only of a plurality of different foreign, short-wave radio transmitting stations and several of said dot-like means being arranged in a plurality of groups, all the members of any one group being equi-distant from a common center and being positioned at intervals along an arc and all of the members of any one group lying in a different arc from those of any other group, a stationary screen having displayed on the front thereof a map 'representing various foreign countries, several of which have a plurality of short-wave radio transmitting stations located therein, said latter screen having a single perforation only in the map portion thereof that represents a particular country having a plurality of transmitting stations located therein and which stations are represented on s aid rotatable screen, means rotatable in consonance with the movement of the rotatable screen for rotating said tuning element, intermediate gearing between said rotatable screen and the shaft'of the tuning element, whereby a 180 rotation of the tuning element effects a 360 rotation of that screen, illuminating means disposed to the rear of said rotatable screen, reflector means associated with said illuminating means and marginal bands carried by said rotatable screen having displayed thereon indicia representing the frequencies and call-letters, respectively, corresponding to diil'erent foreign stations which it is desired to identify. i

3. In a radiol receiving set, the combination with the shaft of a variable tuning element of a rotatable screen having several groups of apertures, the members of each group thereofbeing equi-distant from the center of rotation of said screen kancl at a different distance therefrom. than are the members of another group of such apertures, a stationary map screen having a relatively limited number of apertures as compared with those in said rotatable screens and not exceeding about one to each foreign country represented on such map screen and the arrangement of the respective apertures in the rotatable screen boing correlated to those in stationary map screen so that eaeh of the apertures in the rotatable screen may be brought successively into register with some one of the apertures in the map screen, means for rotating said rotatable screen simultaneously with but at a greater speed of revolution than said shaft of the tuning element and means for projecting a beam of light through two registering apertures in the respective screens.

4. In a radio receiving set, the combination with the shaft of a variable tuning element of a rotatable screen having a plurality of groups of apertures extending therethrough, all the apertures of each group being disposed equi-distant from the center of such screen and at a different distance from such center than are the apertures of any other group thereof, said screen being geared to move through at least a major portion of a complete revolution while the tuning shaft is moving through a minor portion of a complete revolution, a stationary map screen intimately associated with the former screen and which include along their periphery all the perforations of the rotatable screen.

5. In a radio receiving set, the combination with a variable tuning element of visual indicator means for identifying a particular short- Wave transmitting station received by the observer, the same including a rotatable movable screen having a plurality of groups of apertures arranged on said screen in concentrically disposed relation to each other, each group representing a plurality of short-wave transmitting stations of a particular country only, a source of light disposed at one side of said Screen for providing illumination for said screen'and adapted when illuminated to project light beamsthrough all of said apertures simultaneously, a map screen disposed immediately adjacent the former screen and on the opposite side thereof from said light source, said map screen having an extremely restricted number of perforations therethrough as compared with the number on the other screen andthe number of such perforations on such map screen approximately corresponding to but a single perforation for each country whose short-Wave transmitting stations are represented by perforations on the other screen and means to move said movable screen in consonance with the movement of the tuning element to effect registration between one of the apertures on each screen and to thereby admit of the projection from said'light source of a, beam of light through such registering ap ertures to the eye of an observer` 6. In a radio receiving set, the combination with a variable tuning element of visual indicator means for identifying a particular short-wave transmitting station received by the observer,

same including a translucent screen of a selected color, other than white, having a plurality of groups of apertures arranged on said screen in concentrically disposed relation to each other, each group representing aplurality of short- Wave transmitting stations of a particular country only, a source of light disposed at one side of said screen for providing illumination for said screen and adapted when illuminated to project light beams through all of said apertures simultaneously, a map screen disposed immediately adjacent the former screen and on'the opposite side thereof from said light source, said map screen having an extremely restricted number of perforations therethrough as compared with the number on the other screen and the number of such perforations on such map screen approximately corresponding to but a single perforation for each country Whose short-wave transmitting stations are represented by perforations on the other screen and means to Vmove said movable screen in consonance with the movement of the tuning element to effect registration between one of the apertures on each screen and to thereby admit of the projection from said light source of a beam of light through such registering apertures to the eye of an observer.

7. In a radio receiving set, the combination with a variable tuning element of visual indicator means for identifying a particular short-wave transmitting station received by the observer,

the same including a rotatable movable screen' having a plurality of groups of apertures arranged on said screen in concentrically disposed relation to each other, each group representing a plurality of short-wave transmitting stations of a particular country only, a source of light disposed at one side of said screen for providing illumination for said screen and adapted when illuminated to project light beams through all of said apertures simultaneously, a map screen dis-l posed immediately adjacent the former screen and on the opposite side thereof from said light source, said map screen having an extremely restricted number of perforations therethrough as compared with the number on the other screen and the number of such perforations on such map screen approximately corresponding to but a single perforation for each country whose short-Wave transmitting stations are represented by perforations on the other screen and means to move said rotatable screen in consonance with the movement of the tuning element to effect registration between one of the apertures on each screen and to thereby admit of the projection from said light source of a beam of light through such registering apertures to the eye of an observer.

8. In a radio receiving set, the combination with a variable tuning element of visual indicator means yfor identifying a particular shortwave transmitting station received by the observer, the same including a rotatable movable screen having a plurality of groups of apertures arranged on said screen in concentrically disposed relation to each other, each group representing a plurality of short-wave transmitting stations of a particular country only, a source of light disposed at one side of said screen for providing illumination for said screen and adapted when illuminated to project light beams through all of said apertures simultaneously, a map screen disposed immediately adjacent the former screen and on the opposite side thereof from Said light source, said map screen having therethrough as compared with the number on the other screen and the number of such perforations on such map screen approximately corresponding to but a single perforation for each country whose short-wave transmitting stations are represented by perforations on other screen and means to move said movable screen in consonance with, but at twice the rate of rotation of, the tuning element.

9. In a radio receiving set, having a variable tuning element having a rotatable shaft, the sub- `combination comprising geographic station indicator means including a screen movable with said tuning element and having a plurality of groups of apertures extending therethrough, said groups being disposed in concentric relation to each other and all the apertures of each group corresponding in position to and representing a plurality of transmitting stations in a different country from that represented'by any other such group of apertures and means for rotating said screen in consonance with but at a greater rate of revolution than that of said shaft of said tuning element.

10. In a radio receiving set as claimed in claim 1, wherein the center of rotation of the rotatable screen is disposed at a considerable distance from the center of the map screen.

11. In a radioreceiving set, the combination with a variable tuning element, including a rotatable shaft, of visual indicator Vmeans for identifying a particular transmitting station received by the observer, the same including a rotatable translucent screen having a plurality of groups of dot-like means arranged on said screen, each group representing a plurality of transmitting stations of a particular country only ,the members of each group being disposed along an arcuate path and which path is different from that along which the members 'of any other group are disposed, a source of light disposed at one side of said screen for providing illumination for said screen and adapted when illuminated to project light beams through substantially all portions of said screen simultaneously, a map screen disposed immediately adjacent the former screen and on the opposite side thereof from said light source, said map screen having an extremely restricted number of perforations therethrough as compared with the number of dot-like means on the other screen and the number of such perforations on such map screen approximately corresponding to but a single perforation for each separate group of dot-like means on the other screen and means to move said movable screen at a rate of rotation at least about twice that of the shaft of the tuning element.

12. In a radio receiving set as claimed in claim 11, wherein the center of rotation of the rotatable screen is disposed at a considerable distance from the center of the map screen.

13. A radio receiving set as claimed in claim 2. wherein the center of rotation of the rotatable screen is disposed at a considerable distance from the approximate center of the map screen, whereby a wide band spread of the transmitting stations represented on the rotatable screen is obtained and as a consequence the visual indicator means is rendered highly selective and comparable with the audible tuning selectivity of a highly selective set.

l 14. A radio receiving set as claimed in claim 8, wherein the center of rotation of the rotatable screen is disposed at a considerable distance from the approximate center of the map screen, whereby a wide band spread of the transmitting stations represented on the rotatable screen is obtained and as a consequence the visual indicator means is rendered highly selective and comparable with the audible tuning' selectivity o a highly selective set.

15. In a radio receiving set, the combination with the shaft of a variable tuning element of a rotatablescreen formed of translucent material of a selective color and having a plurality of dotlike means each member thereof representing a different radio transmitting station which it may be desired to receive. certain members of said dot-like means being arranged in a plurality of groups and the members oi" each group being positioned along a common arcuate path and which path is diilerent from that along which the members of any other group are positioned and the other of said screens being stationary and having a plurality of the radio transmitting stations of one particular country, which stations it is desired to identify, represented by a single aper-V ture which is common to those transmitting stations of that country, only, and each of such apertures of such stationary screen being so f disposed thereon that at some period during the:

said stationary screen, a light source for illuminatlng the translucent movable screen during the time that the observer is seeking to identify a particular station andmeans for rotating said movable screen at a substantially greater rate of rotation than said tuning shaft.

16. A radio receiving set as claimed in claim 15, wherein the center of rotation of therotatable screen is disposed at a considerable distance from the approximate center of the map screen, whereby a wide band spread of the transmitting stations represented on the rotatable screen is obtained and as a consequence the visual indicator means is rendered highly selective and comparable with the audible tuning selectivity of a highly selective set.

KARL BIEGLER. 

